Automobile seats, in particular single seats, are generally constructed so as to be adjustable. Here, on the one hand, the seat as a whole can be longitudinally adjustable, for which a seat part of the automobile seat is fastened to an upper track and the upper track is longitudinally displaceable with respect to a lower track fastened on the automobile side.
In addition, usually a backrest part of the automobile seat is swivelably articulated on its seat pan part. The articulation is produced here by fittings which have components on the seat pan part side and also on the backrest part side, which are swivelable or rotatable relative to each other. Several different types of fitting exist for this; detent fittings or tumble fittings are frequently used.
Either a manual or a motor-driven adjustment movement can be provided to carry out the movements of the automobile seat. To produce motor drive motions, generally electric motors are used, in particular electric direct current motors, owing to the direct current network in motor vehicles. As such direct current motors usually provide drive motions with high rotation speeds, which are not able to be used directly as an adjustment movement, a reduction takes place by means of the gearbox. With the reduced movement, the seat or respectively a seat component is adjusted.
In particular for memorized seat functions, such as for example in the case of a stored longitudinal position of the seat with respect to the lower track of the seat or a particular backrest inclination, the electric motors have detection means in order to be able to establish the number of revolutions and/or rotation speed of the motor. This information is used by a control of the seat adjusting device, in order to transfer the seat or its components into the desired stored position. In particular with a plurality of different seats, this can lead to a large number of different electric motors, which involves high costs. In the previously known solutions, in addition it is a disadvantage that owing to the high rotation speeds of the electric motors used hitherto, high scanning frequencies are necessary, which in turn lead to a large amount of data which are to be processed, which in turn make high-performance and expensive evaluation electronics necessary. Furthermore, through the high frequencies, high electromagnetic loads occur, which in turn entail a high expenditure to achieve an immunity to interference in the respectively adjacent assemblies.
Such a seat adjusting device, in which the motor rotation speed is detected and the position of the automobile seat is calculated therefrom, is disclosed in DE 3527906 A1.